Glycoprotein hormones (TSH, LH, FSH, CG) each contain a common Alpha subunit combined with a unique Beta subunit to form the active hormone. The Alpha and Beta subunits are homologous and the alpha subunit is always present in molar excess in normal pituitary. This is analogous to hemoglobin synthesis which requires the coordinate expression of the alpha globin gene with an additional homologous gene (Beta, Gamma, Delta, Epsilon) to produce a functional hemoglobin molecule.